Which of the following is the most ecologically relevant environmental factor?

Temperature is the most important and relevant ecological factor. The developmental, morphological, as well as physiological functions of both the flora and fauna are directly or indirectly dependent on temperature. Sometimes, they may even be governed by the temperature.

For example, in the case of reptiles, temperature is the only crucial factor that determines the sex of the offspring. High temperatures favour female births while low temperatures favour male births.